Detection of paralytic shellfish toxins (PSTs) in bivalve shellfish by analytical methods is complicated and costly, requiring specific expertise and equipment. Following extensive blooms of Alexandrium tamarense Group 1 in Tasmania, Australia, an investigation was made into commercially available screening test kits suitable for use with the toxin profiles found in affected bivalves. The qualitative Neogen rapid test kit, with a modified protocol to convert gonyautoxins GTX1&4 and GTX2&3 into neosaxitoxin and saxitoxin (STX), respectively, with higher cross-reactivities, was the best fit-for-purpose. This validation study of the test kit and the modified protocol was undertaken following AOAC INTERNATIONAL guidelines for the validation of qualitative binary chemistry methods. The validation used four different PST profiles representing natural profiles found in Australia and in Europe: two in a mussel matrix and two in an oyster matrix. The test kit was shown to have appropriate selectivity of the toxin analogs commonly found in bivalve shellfish. The matrix and probability of detection (POD) study showed that the rapid test kit used with the modified protocol was able to consistently detect PST at the bivalve regulatory level of 0.8 mg STX⋅2HCl eq/kg, with a POD estimated via the binomial logistic regression of 1.0 at 0.8 mg STX⋅2HCl eq/kg in all tested profiles in both matrixes. The POD at 0.4 mg STX⋅2HCl eq/kg was 0.75 and 0.46 for the two toxin profiles in an oyster matrix and 0.96 and 1.0 for the two toxin profiles in a mussel matrix. No significant differences in the PODs of the PSTs at the regulatory level were found between production lots of the test kits. The results suggest the method is suitable to undergo a collaborative validation study.